An airbag device is provided in which an airbag having a left airbag section and a right airbag section is folded by a new folding method. An airbag includes a left airbag section inflated on the left in front of a passenger; a right airbag section inflated on the right in front of the passenger; and a base chamber that connects ends of the left airbag section and the right airbag section. When the left airbag section and the right airbag section are folded, the lower halves of the bags and from a connecting band are folded back upward along a line L1 that connects the lower edge of the connecting band and the lower edge of the fixing plate.